1. Field of the Invention
The present invention relates to a method for fusion splicing optical fibers, and an optical fiber transmission line obtained by the method. More particularly, the method includes a fusion splicing process in which fusion splicing is performed by butting the end faces of two optical fibers together and a heat treatment process in which a fusion-spliced part and the vicinity thereof are heated.
2. Description of the Background Art
In the case of optical fibers having smaller or different mode field diameters, fusion splicing is performed by butting end faces of two optical fibers, and the fusion spliced part and the vicinity within several mm of both sides thereof are subjected to heat treatment such that a dopant in the optical fibers is diffused so as to decrease the differences in the refractive index profiles of the fusion spliced part and thereby lessening the splicing loss.
The heat source of a heating unit used in the heat treatment process is generally a plurality of micro burners arranged suitably in relation to the optical fibers. The heating unit must be prepared in addition to an arc unit used for fusion splicing. If the arc unit is also used for heat treatment of optical fibers, a fusion splicing process and a heat treatment process could be done with one unit. However, it is difficult to adjust the heating amount by the discharge electric current itself because it is essential to provide the arc unit with an electric current that is larger than a trigger electric current with which the puncture of the air insulation occurs. It is possible to consider adjusting the amount of heat by performing electric discharge while shifting the position of the arc heating along the optical fiber. It is necessary to make the highest diffusion of the dopant at the fusion-spliced part, decreasing the degree of such diffusion gradually as the location is more distanced from the fusion-spliced part. However, such heat treatment method has a disadvantage in that an excessive heating easily occurs at a turning point because the movement stops at each turn, which results in excessive diffusion of the dopant at the turning point of the movement that is distanced from the fusion-spliced part. In consequence, the optical loss of the optical fibers is increased, causing an increase in the splicing loss.